The present invention relates generally to rotating labyrinth seals and particularly to rotating labyrinth seals used in gas turbine engines for the propulsion of aircraft.
Rotating labrinth seals have a wide variety of uses and one such use is to effect sealing between plenums at different pressures in gas turbine engines. Such seals generally consist of two principal elements, i.e., a rotating seal and a static seal. The rotating seal, in cross section parallel to the axial length of the engine, frequently has rows of thin tooth-like projections extending radially from a relatively thicker base toward the static seal. The static seal or stator is normally comprised of a thin honeycomb ribbon configuration. These principal elements are generally situated circumferentially about the axial (lengthwise) dimension of the engine and are positioned with a small radial gap therebetween to permit assembly of the rotating and static components.
When the gas turbine engine is operated, the rotating seal expands radially more than the stator and rubs into the stator seal. The thin honeycomb ribbon construction of the stator reduces the surface area on which the seal teeth rub and thus helps to minimize the heat transferred into the rotating seal. In addition, the rotating seal teeth tips are made thin in order to thermally isolate them from the supporting base or shell structure.
The thin tooth configuration is, however, susceptible to handling damage which can result in cracks in the tips of the teeth opposite the base. In some cases, rub-generated cracks during operation may also be formed on the tooth tips. These seal tooth cracks propagate through the teeth radially inward into the supporting shell structure and, left undetected, can eventually spread toward the ends of the support structure resulting in failure of the seal.
The cross-sectional configuration of the seal teeth in the prior art is generally one of a truncated triangular configuration with straight sloping sides meeting at a thin, flat tip. Such prior art configurations of the seal teeth have provided insufficient stalling or arresting of such cracks once they have begun.